JP3609959B2 - Screen bowl type decanter type centrifuge - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention has an outer rotating cylinder and a screw conveyor provided in the outer rotating cylinder so as to be relatively rotatable, and the outer rotating cylinder is provided on a solid discharge side from a parallel portion having a large diameter and the parallel portion. A small-diameter parallel portion and an inclined portion connecting the parallel portions. The small-diameter parallel portion has a filtrate discharge hole formed therein, and a cylindrical filter medium is provided on the inner wall of the parallel filter section. And a screen bowl type decanter type centrifugal separator provided with a cleaning nozzle for cleaning the processed material at the portion of the filter medium part.
[0002]
[Prior art]
An example of a conventional decanter centrifuge is shown in FIG. The centrifuge shown in the figure is commonly referred to as a solid bowl type, and has a large-diameter parallel portion 1 provided with a clarification liquid overflow port 5 called a dam at the left end and a right end connected to the large-diameter parallel portion 1. It has an outer rotating cylinder 4 which rotates at a high speed and is formed of a sloped part 2 including a so-called beach provided with a solid material discharge port 6, and is spirally held inside the outer rotating cylinder 4 with a slight radial clearance. A screw conveyor 7 having a conveyor blade 8 is provided so as to be relatively rotatable.
[0003]
When a processed product slurry comprising a crystalline solid and a solvent is introduced into the solid bowl centrifuge, the crystalline solid that is a processed product is removed from the outer rotating cylinder 4 by centrifugal force caused by rotation as shown in FIG. The crystalline solid matter that settles on the inner wall surface and adheres impurities in the process product generation process or the solvent of the process slurry on the surface is on the same axis as the outer rotating cylinder 4. The screw conveyor 7 that rotates at a speed different from that of the outer rotating cylinder 4 is sent to the inclined portion 2 and is subjected to a liquid removal action at the inclined portion 2 that has gone up the beach. A part of the crystalline solid that cannot be settled with the solvent forming the treated slurry overflows from the overflow port 5 provided at the left end of the large-diameter parallel portion 1 and is discharged to the outside.
[0004]
The crystalline solid matter discharged from the solid bowl centrifuge generally has impurities produced in the production process of the product crystal, or the solvent itself attached to the crystal surface. In order to reduce the degree of adhesion of this impurity or solvent, a method of increasing the product purity by repeating solid-liquid separation several times by re-slurrying with a fresh solvent or replacing with another solvent is taken. It is normal. In this way, when using a centrifuge for the purpose of lowering the degree of adhesion of impurities or solvent adhering to the surface of the crystalline solid, and further performing liquid removal, the washing solvent is used for washing the crystalline solid. 9 may be mixed with a separation liquid as a processing solvent, as shown in FIG. 9, a cleaning chamber 13 is provided inside the conveyor at the site of the inclined portion 2 where the beach is raised, and the processing slurry is supplied to the outer rotating cylinder 4. A cleaning liquid passage 12 is provided in a part of a fixed feed tube 11 that is guided into the interior, the cleaning liquid is guided into the cleaning chamber 13 from the outside, and the inclined portion 2 is fixed by a cleaning liquid nozzle 14 or the like attached to the conveyor drum 9. In general, it is common practice to wash the crystalline solid material, which is a processed product, with a cleaning liquid such as water that does not contain impurities.
[0005]
However, in order to enhance the cleaning effect, if the cleaning liquid is continuously applied to the processed material from the upper part of the inclined portion 2 that rises on the beach to the vicinity of the solid material discharge port 6, the degree of liquid removal of the product crystals deteriorates. Although it is conceivable to limit the washing to the crystal immediately after it comes out of the liquid layer or close to it, the time for the washing liquid to contact the crystal is short, so the product purity is improved to some extent, but the number of separator stages can be reduced. The actual cleaning effect is not as good.
[0006]
As shown in FIG. 10, as shown in FIG. 10, a small-diameter parallel part 3 is provided in connection with an inclined part 2 that rises on the beach, in order to improve the liquid crystal drainage and the cleaning effect in the solid bowl centrifuge. A large number of filtrate discharge holes 3a are formed in the parallel part 3 having a small diameter, and a cylindrical filter medium 3b such as a bar screen is disposed on the inner wall thereof to constitute the filter medium part 10, and centrifugal filtration is performed in the filter medium part 10. Such a centrifuge has already been developed, which is commonly called a screen bowl centrifuge. In this screen bowl type centrifuge, a filter medium such as a mesh screen or porous ceramic can be used as the cylindrical filter medium 3 b in the filter medium section 10.
[0007]
In the screen bowl type centrifuge, the processed material slurry introduced from one end of the outer rotating cylinder 4 via the feed tube 11 is subjected to centrifugal force in the large-diameter parallel portion 1 of the outer rotating cylinder 4 rotating at high speed. The crystalline solid and the separated liquid are separated and sent to the inclined portion 2 by the screw conveyor 7, and the crystalline solid that has gone up the beach is subjected to a liquid removal action at the portion of the inclined portion 2 to be separated into solid and liquid. The separation mechanism is the same as that of the solid bowl type described above, but the bowl has two stages of a large-diameter parallel part 1 and a small-diameter parallel part 3, and the inner wall of the small-diameter parallel part 3 The filter medium part 10 is formed by holding the cylindrical filter medium 3b, and a part of the feed tube 11 described above is formed at the start of the small-diameter parallel part 3 based on the structure. Cleaning fluid passage In the cleaning chamber 13 inside the conveyor, the crystalline solid is washed by applying the cleaning liquid to the crystalline solid by the cleaning liquid nozzle 14 attached to the conveyor drum 9 and the like. Furthermore, it is possible to remove the liquid adhering to the surface of the crystalline solid in the latter half of the filter medium part 10 in the small-diameter parallel part 3. The cleaning liquid containing the liquid adhering to the crystal surface by this cleaning action passes through the filtration opening of the filter medium 3b in the filter medium section 10 and passes through the filtrate discharge hole 3a or slot provided in the small-diameter parallel section 3 to the outside of the centrifuge. Discharged.
[0008]
As described above, in the screen bowl type centrifuge, in addition to the primary drainage at the inclined portion 2 that goes up the beach, the parallel drainage 3 is subjected to the filtration drainage by the secondary drainage at the filter medium portion 3b. Therefore, if the crystal shape is relatively round and the processed material is easy to move on the surface of the filter medium in a simple surface state, or if the crystal is matched with the filter medium such as a processed material in which the crystal is easily dissolved by the cleaning liquid, In terms of performance, it shows superior performance compared to the solid bowl type.
[0009]
[Problems to be solved by the invention]
However, in the screen bowl type centrifuge, in order to perform filtration drainage with the filter medium part 10 in the parallel part 3 with a small diameter, pay attention to the physical properties such as the crystal grain size, shape, and wear properties, and select the filter medium 3b. In addition to the necessity to do so, it is inevitable that there is crystal escape from the filter medium part 10 as long as the filter medium is filtered. In order to reduce this crystal escape as much as possible, a bar screen with a small opening When the mesh screen is used, crystals are clogged in the filtration opening of the filter medium 3b, and the filtration can be performed only for a short time. This causes a problem that the filtration unit 10 cannot be used effectively. This crystal escape resulted in a deterioration of the crystal recovery efficiency compared to the solid bowl centrifuge.
[0010]
In addition, since a radial gap is provided between the conveyor blade 8 of the screw conveyor 7 and the inner wall surface of the filter medium part 10, it is inevitable mechanically that a residual layer with a certain thickness is formed, Even if the thickness of the remaining layer is slightly increased, an effort has been made to make the remaining layer easy to move by appropriately selecting the filter medium 3b having a small friction coefficient on the surface depending on the internal friction of the crystalline solid particles.
[0011]
On the other hand, as shown in FIG. 11, the conveyor blade 8 for conveying the crystalline solid matter facing the filter medium portion 10 in the small-diameter parallel portion 3 is partially cut away, and the radial direction between the conveyor blade 8 and the inner wall of the filter medium portion 3b. In the case of a structure having a large gap, the crystalline solid material sent by the screw conveyor 7 remains on the plane formed by this gap, and a residual layer D is formed, and is not sent by the conveyor blade 8. Although the portion of the remaining layer D varies depending on the physical properties such as the transportability of the crystalline solid matter by the conveyor blade 8, it becomes compacted when the stagnation time becomes long, and the cleaning liquid cannot pass therethrough. It was not necessarily effective for all crystalline solids to have a large thickness. When the thickness of the residual layer D is increased, the stagnant crystalline solid is a state of crystal filtration in which most of the crystals conveyed by the conveyor blade 8 prevent the crystalline solid from escaping from the filter medium part 3b. On the other hand, if the residual crystalline solid remains stagnant at the same position, the residual crystal is consolidated by the centrifugal force due to the rotation and by the contact of the end face of the conveyor blade 8, and as a result, the residual crystal There has been a problem that the filtration effect of the layered crystalline solid is impaired. That is, in the case of the screen bowl type centrifuge, the problem of the escape of the crystalline solid from the filtration opening of the filter medium 3b in the filter medium part 10 and the problem of the reduction of the liquid removal effect due to the residual layer compaction occurred.
[0012]
This is true not only for the screen bowl type but also for decanter type centrifuges in general. The radial clearance between the conveyor blades 8 of the screw conveyor 7 and the inner wall of the small-diameter parallel part 3 is the same as that of the screw conveyor 7 and the outside rotation. As long as the cylinder 4 rotates at a different speed, it is absolutely necessary. However, the residual layer D has a higher filtering effect due to washing in the case of the thin gap b than in the case of the thick gap a. In general, it is advantageous to make the gap as small as possible. However, if the thickness of the remaining layer D is too thin, as shown in FIG. 12, the height H of the transport cross-sectional area of the crystalline solid material conveyed by the conveyor blade 8 becomes large, and the cleaning liquid becomes a crystalline solid material. This causes a problem that the cleaning effect is diminished because it is discharged to the outside through the remaining layer by the thin gap b.
[0013]
The present invention has been made in view of the above-described problems, and its purpose is to form a filtrate discharge hole in a small-diameter parallel portion of the outer rotating cylinder, and to dispose a cylindrical filter medium on the inner wall of the filter medium section. In the screen bowl type decanter type centrifuge provided with a cleaning nozzle for cleaning the processed material at the filter medium part, the screw conveyor at the filter medium part is improved, and the filter medium part The washing solvent for the crystalline solid moving on the surface can be separated from the treated solvent and taken out of the machine. At this time, the crystal is continuously and stably filtered to escape into the filtrate. By reducing the amount of crystalline solids as much as possible, the recovery rate of crystalline solids is increased, and by selecting a relatively large filtration opening for the filter medium, impurities can be washed without causing internal clogging of the crystalline solids. Effect It can gel, simplified function is to provide a screen bowl type decanter centrifuge which attained the peripheral facilities reduced.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the screen bowl type decanter type centrifuge according to the present invention is characterized by what is described in each claim, and in particular, claim 1 as an independent claim. The screen bowl type decanter centrifuge according to the invention has an outer rotating cylinder and a screw conveyor provided in the outer rotating cylinder so as to be relatively rotatable, and the outer rotating cylinder includes a large-diameter parallel portion; The parallel portion includes a small-diameter parallel portion provided on the solid discharge side and an inclined portion connecting the parallel portions, and the small-diameter parallel portion has a filtrate discharge hole formed therein, and has a cylindrical shape on its inner wall. In a screen bowl type decanter type centrifuge in which a filter medium part is arranged to form a filter medium part and a cleaning nozzle is provided for cleaning the processed material in the filter medium part. A Lieu conveyor is disposed between a main conveyor having a large radial gap between the conveyor blade and the inner wall of the filter medium part, and between the pitch of the main conveyor, the conveyor blade and the inner wall of the filter medium part; It is comprised by the at least 1 sub conveyor which made the radial direction space | interval of between smaller than that of the said main conveyor.
[0015]
[Action]
According to the present invention, the primary and secondary conveyors in the filter medium part formed in the parallel part having a small diameter are continuously rotated from the conveyor feed port by always performing relative rotation with the outer rotating cylinder, and the radial clearance between them. In contrast to the main conveyor blade that has a large clearance, the secondary conveyor blade has a smaller radial gap between it and the inner wall of the filter medium. As a result, each conveyor blade imparts an axial conveying force to the crystalline solid by the difference in the gap. Both the primary and secondary conveyor blades have the same axial conveying force as that sent by a single conveyor blade, and are not continuously exposed to the centrifugal force field, but are pressed by the end of the conveyor blade. Without being compacted, it is washed with the washing liquid in the form of transporting the smoothed crystalline solid.
[0016]
As shown in FIG. 12, the conventional conveying form of one conveyor blade is sent in a state where the portion pushed by the conveyor blade is high and is almost in the shape of a height H, so that the cleaning liquid flows down the triangular slope, It flows into the thinner remaining layer portion. On the other hand, when both the primary and secondary conveyor blades according to the present invention as shown in FIG. 5 are used, the crystal cleaning is performed by providing the cake cleaning nozzle 14 between the respective conveyor blades 8a and 8b. Then, since the surface on which the cleaning liquid is applied is smoothed as compared with the case of FIG. 12, the cleaning liquid penetrates into the conveyed crystalline solid, and cleaning can be performed more effectively. Further, when the flat crystal layer has a filtering effect, it is possible to further reduce the escape of crystals from the filter medium.
[0017]
Further, in this crystal filtration state, an opening having a larger opening than the crystal grain size can be selected, and washing and draining can be performed without blocking the crystal in the opening.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIGS. 1 to 5 as follows. In addition, the following example demonstrates what has set the number of the conveyor blade | wings in the site | part of the filter medium part 10 comprised in the parallel part 3 of small diameter as 2 sheets of the main conveyor blade | wing 8a and the sub conveyor blade | wing 8b.
[0019]
The screen bowl type centrifuge according to the present embodiment has an outer rotating cylinder 4 and a screw conveyor 7 provided in the outer rotating cylinder 4 so as to be relatively rotatable, and the outer rotating cylinder 4 has a large-diameter parallel portion. 1, a small-diameter parallel portion 3 provided closer to the solid material discharge port 6 than the parallel portion 1, and an inclined portion 2 that connects both the parallel portions 1 and 3. A filter discharge hole 3a is formed on the inner wall, and a cylindrical filter medium 3b is disposed on the inner wall thereof to constitute a filter medium part 10, and a cleaning nozzle 14 for cleaning the processed material in the filter medium part 10 is provided. In the bowl-type centrifuge, the screw conveyor 7 in the filter medium part 10 is arranged between the main conveyor having a large radial gap a between the conveyor blade 8a and the inner wall of the filter medium part 10, and the pitch of the main conveyor. Arranged It is composed of duplicate two conveyors with one sub-conveyor that is smaller than the radial gap b between the conveyor blades 8b and the inner wall of the filtration portion 10 on it of the main conveyor.
[0020]
As shown in FIG. 3, the radial direction of the conveyor blade relative to the filter medium part 10 should be shortened by an appropriate height so that an appropriate remaining layer thickness can be obtained, assuming that it is continuous with the conveyor blade 8 of the screw conveyor 7. The main conveyor blades 8a that maintain a large radial clearance with the filter medium part 10 are arranged.
[0021]
Further, as a secondary conveyor, the secondary conveyor blades 8b having a small radial clearance are wound between the pitches of the main conveyor blades 8a having a large radial clearance as shown in FIG. Only the portion in the radial gap a of the main conveyor blade 8a having a large directional gap is not conveyed until the other sub-conveyor blade 8b having a smaller radial gap is rotated. The remaining layer formed by the main conveyor blades 8a having a large radial gap with the notches is sent by the other sub-conveyor blades 8b having a small radial gap, and the crystal conveyance mode is shown in FIG. As shown in the figure, the conveyor blades are smoothed more than the single crystal conveyance mode shown in FIG.
[0022]
The main conveyor blade 8a having a large radial clearance, the sub-conveyor blade 8b having a small radial clearance, and the cleaning liquid nozzle 14 are disposed as shown in FIG.
[0023]
The notch height of the main conveyor blade 8a having a large radial gap and the radial gap a determine the feed crystal amount of the other conveyor vane blade 8b having a small radial gap without the other notch. The crystal feed heights of the two main and sub conveyor blades 8a and 8b are determined to be approximately the same. Further, the interval between the respective conveyor blades 8a and 8b is such that, as shown in FIG. 6, if the crystal forms a bridge E between the conveyor blades 8a and 8b, it cannot be transported. It is necessary to determine the pitch interval, which is appropriately determined by design taking into consideration the physical properties of the crystalline solid.
[0024]
In this situation, as shown in FIG. 12, the crystal transfer mode is smoothed compared to the crystal transfer mode of the screw conveyor consisting of only one conveyor blade 8 of the same pitch, and the area of the crystal filtration portion is reduced. The widening of the cleaning liquid uniformly penetrates into the crystal layer, and an effective crystal cleaning effect is obtained. Further, as shown in FIG. 5 as compared with FIG. 12, since the thin portion b of the remaining layer is narrow, the crystal filtration portion can be widened, and the escape of crystals from the filter medium portion 10 can be reduced. .
[0025]
In addition, when the conveyor blade pitch interval is sufficiently wide, in addition to the main and sub two conveyor blades 8a and 8b, in addition to the radial gaps in FIG. If the second sub-conveyor blade 8c that is set to be large in a staircase shape is provided, it is expected that the crystal conveyance form is further smoothed and the cleaning effect is enhanced.
[0026]
On the other hand, in the case of only the conveyor blade 8 having a slightly larger radial gap as shown in FIG. 12, it is possible to make the remaining layer portion of the crystal, and it seems that crystal filtration is possible on the entire surface of the filter medium 3a. Since the force that pushes the residual layer portion of the crystal in the axial direction is only the shearing force between the conveyor blades 8 and the crystalline solid material and is weak, if the radial gap is increased, the residual layer portion becomes the inner wall surface of the filter medium portion 10. Result in stagnation at the same position, and as described above, it is consolidated and the filtration effect is significantly reduced.
[0027]
In addition, as shown in FIG. 2, when the cleaning portion is set as the conveyance start portion at the site of the filter medium portion 10, a portion that is not cleaned is provided in the latter half portion, and the crystal surface replaced with the cleaning liquid in this portion. If liquid removal is performed, it is possible to further reduce the remaining impurities.
[0028]
【The invention's effect】
Product crystals produced in the chemical and food industries have unpolymerized substances and a solvent constituting a slurry attached to the crystal surface during the production process. This deposit can be washed and replaced with certain other solvents. According to the present invention in which a plurality of conveyor blades having different radial gaps are used at the portion of the filter medium portion in the screen bowl type centrifuge, the crystal moving on the surface of the filter medium is applied by a cleaning liquid nozzle provided on the conveyor cylinder. The washing solvent can be separated from the treated solvent and taken out of the centrifuge, and crystal filtration can be performed more continuously and stably than the conventional machine of this type by improving the screw conveyor. The crystal recovery rate can be increased by minimizing the escape amount of crystals in the filtrate, and the filtration opening of the filter medium can be made relatively large. The effect of simplification of functions and reduction of peripheral equipment can be obtained.
[Brief description of the drawings]
FIG. 1 is a side sectional view of a screen bowl centrifuge according to an embodiment of the present invention.
FIG. 2 is a partial cross-sectional view in which cleaning liquid nozzles are disposed between main and sub conveyor blades at a conveyance start portion at a filter medium portion according to an embodiment of the present invention.
FIG. 3 is a side view of a screw conveyor disposed in an outer rotating cylinder including a large-diameter parallel portion, an inclined portion, and a small-diameter parallel portion according to an embodiment of the present invention.
FIG. 4 is an explanatory diagram of two main and sub conveyor blades in a screw conveyor according to an embodiment of the present invention.
FIG. 5 is an explanatory diagram of a crystal conveyance form by main and sub two conveyor blades in the embodiment of the present invention.
FIG. 6 is an explanatory diagram of a crystal transport mode when the pitch is narrow by the main and sub two conveyor blades.
FIG. 7 is an explanatory diagram of a crystal conveyance mode by a main 1 sheet and sub 2 sheet three conveyor blades in another embodiment of the present invention.
FIG. 8 is a side sectional view of a solid bowl centrifuge according to the prior art.
FIG. 9 is a partial cross-sectional view showing solids cleaning on an inclined beach in a solid bowl centrifuge.
FIG. 10 is a cross-sectional side view of a single conveyor blade screen bowl centrifuge according to the prior art.
FIG. 11 is a partial cross-sectional view showing a remaining layer formed in a filter medium part in a single conveyor blade screen bowl type centrifuge.
FIG. 12 is an explanatory diagram of a crystal conveyance form by a single conveyor blade in the filter medium part.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Large-diameter parallel part 2 ... Inclined part 3 ... Small-diameter parallel part 3a ... Filtrate discharge hole or slot 3b ... Filter medium 4 ... Outer rotating cylinder 5 ... Clear liquid overflow port 6 ... Solid matter outlet 7 ... Screw conveyor 8 ... Conveyor blade 8a ... Main conveyor blade 8b ... Sub-conveyor blade 8c ... Second sub-conveyor blade 9 ... Conveyor cylinder 10 ... Filtering part 11 ... Feed tube 12 ... Washing liquid passage 13 ... Washing chamber 14 ... Washing liquid nozzle

Claims (2)

The outer rotary cylinder has a screw conveyor provided in the outer rotary cylinder so as to be relatively rotatable. It consists of a parallel part and an inclined part connecting both parallel parts. In a screen bowl type decanter type centrifuge provided with a cleaning nozzle for cleaning the processed material at the site of the filter medium part,
The screw conveyor in the filter medium part is disposed between a main conveyor having a large radial gap between the conveyor blade and the inner wall of the filter medium part, and the pitch between the main conveyor, the conveyor blade and the filter medium A screen ball type decanter type centrifuge characterized by comprising at least one sub-conveyor in which a radial clearance between the inner wall of the section is smaller than that of the main conveyor. As the screw conveyor in the part of the filter medium part, between the pitches of the main conveyor having a large radial gap, a plurality of sub-conveyors having the radial gap sequentially increased stepwise in the solid material conveying direction The screen bowl type decanter type centrifuge according to claim 1.

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